Facebook will accept 3 versions of your password

facebook password

Let’s say it’s “pAssword“, the versions that will be accepted are

pAssword” – the password as it is
PaSSWORD” – the password, case inverted, in case you have caps lock on
PAssword” – the password with its first letter capitalized, for those with mobile devices that insist on Capitalizing Everything

The reason this works is because Facebook stores three hashes of your password.